This invention is directed to an improved method for roasting and leaching vanadium-bearing iron ores and/or iron ore concentrates whereby the vanadium-values are extracted from the iron ores and/or iron ore concentrates.
Modern practices for removing vanadium-values from vanadium-bearing iron ores and/or iron ore concentrates include roasting a mixture of the iron ores and/or iron ore concentrates and an alkali metal compound, such as sodium carbonate, sodium sulfate, sodium chloride and the like, and, thereafter, leaching the mixture with water to extract soluble sodium vanadates from the roasted iron ores and/or iron ore concentrates.
Usually the iron ores and/or iron ore concentrates are mixed with soda ash and the mixture is balled prior to roasting. The pellets produced in roasting can contain as much as 2.0% soda (Na.sub.2 O). Leaching the pellets with water extracts sodium vanadates formed during the roasting step. A considerable amount of the alkali, or soda (Na.sub.2 O), forms insoluble compounds with the gangue constitutents present in the ore. As a result, after leaching as much as 1.1% soda (Na.sub.2 O) can remain in the pellets. This percentage of soda is an excessive amount and the pellets cannot be considered for use in a blast furnace because the soda in the pellets will react with the constituents in the refractory lining in the blast furnace causing premature failure of the refractory lining.
Prior art methods are exemplified in U.S. Pat. No. 3,486,842 issued Dec. 30, 1969 to Eugene J. Michal entitled "Process for Removing Vanadium from Iron Ores". The process is directed to grinding a vanadium-bearing iron ore, mixing the ground ore with a sodium or potassium compound such as sodium carbonate and the like, forming the mix into nodules or pellets, heating the pellets in an oxidizing atmosphere to 700.degree.-1950.degree. F., raising the temperature to 2200.degree.-2450.degree. F. and further heat treating the pellets to harden the pellets and to form water soluble alkali metal vanadates. The pellets are leached in water to extract the alkali metal vanadates which dissolve in the water. The vanadate-rich water is separated from the pellets and the vanadium-values are recovered by known methods.
Unfortunately, as previously noted above, the described process does not remove all the alkali from the pellets. As a result, the pellets are not usable in the blast furnace to recover the iron-values therein, since the alkali reacts with constituents in the refractory lining in the blast furnace causing premature failure thereof.
It is the object of this invention to provide an improved method for extracting vanadium-values from vanadium-bearing iron ores and/or iron ore concentrates, which method does not introduce objectionable amounts of alkali into the iron ores and/or iron ore concentrates.
It is another object of this invention to provide a method for extracting vanadium-values from vanadium-bearing iron ores and/or iron ore concentrates wherein the iron ores and/or iron ore concentrates are mixed with a calcium containing material. The mix is roasted in an atmosphere containing oxygen. The roasted mix is ground and then leached in an aqueous solution containing carbonate or bicarbonate compounds to extract vanadium-values as vanadates which are readily soluble in the aqueous leaching solution and simultaneously produce substantially insoluble calcium carbonate or calcium bicarbonate which remains with the undissolved residue containing iron-values.
It is another object of this invention to provide an improved method for extracting vanadium-values from vanadium-bearing iron ores and/or iron ore concentrates including mixing the iron ores and/or iron ore concentrates with a calcium containing material, roasting the mix in an atmosphere containing oxygen, comminuting the roasted mix and then leaching the comminuted mix in an aqueous solution containing ammonium carbonate or ammonium bicarbonate to thereby extract vanadium-values as ammonium vanadates which are alkali-free. The ammonium vanadates are soluble in the aqueous leaching solution but the calcium carbonate or calcium bicarbonate simultaneously produced during extraction is substantially insoluble in the aqueous leaching solution. The aqueous leaching solution can be easily treated to recover alkali-free vanadium-values.
Broadly, the method of the invention includes mixing vanadium-bearing iron ores and/or iron ore concentrates with a calcium containing material, roasting the mix at a temperature for a time in an atmosphere containing oxygen to form calcium vanadates, comminuting the roasted mix and leaching the roasted comminuted mix in an aqueous solution containing carbonate or bicarbonate compounds whereby vanadium-values in the form of vanadates are extracted from the roasted iron ores and/or iron ore concentrates.